UC Berkeley Press Release

Theodore E. Cohn, vision expert & signal designer, dies

By Liese Greensfelder, Media Relations | 09 June 2006

BERKELEY – Theodore E. Cohn, a University of California, Berkeley, professor of optometry and bioengineering, and a leading researcher in signal detection theory and its real-world applications, died on May 25 at Alta Bates Hospital in Berkeley following a three-year battle with lymphoma. He was 64.

Theodore E. Cohn (Peg Skorpinski photo)

In his 36 years on the UC Berkeley faculty, Cohn's research spanned many fields. From studying how people pick signals out of cluttered backgrounds, to elucidating neural responses to visual input, to applying that knowledge to design improved traffic safety devices, his work was united by the common theme of vision.

"Ted was viewed as a standard-bearer in the field for his analysis that involves beautifully definite, rational and clear ideas about visual processing," said Don MacLeod, a professor of psychology at UC San Diego. "He was a wonderful person to discuss ideas with: he was confident, incisive and clear yet always unassuming and disinclined to impose his ideas on others."

Born in 1941 in Highland Park, Ill., Cohn was the grandson of Lithuanian immigrants. He received a B.S. in electrical engineering from MIT and then attended the University of Michigan, where he received three degrees: an M.S. in bioengineering in 1965, an M.A. in mathematics in 1966, and a Ph.D. in bioengineering in 1969.

In 1970, he was appointed an assistant professor of physiological optics at UC Berkeley, the institution where he would spend his entire professional career. When the campus established a bioengineering department in 1998, Cohn played a major role in its development and was given a joint appointment in bioengineering and optometry.

Cohn's interest in signal detection theory began in college. Both MIT and the University of Michigan were hotbeds of research in the field, which provides models based on precise language and graphic notation for analyzing how people make decisions in the face of uncertain events. (The field emerged during World War II, when the military began to explore how radar operators could detect signals of incoming airplanes in the clutter of background noise on their screens.)

One of Cohn's contributions was to mathematically quantify an ideal human observer and how that observer would react when uncertainty is present, said Stanley Klein, a UC Berkeley professor of optometry. "He did a number of elegant experiments to show that there were important effects if the human didn't know where or when to look," Klein said.

While much of Cohn's experimental work addressed the limits of human visual performance, he also studied the electrical signals passing from the eye to the brain in frogs, cats and locusts, noting that the eye's response to repetitions of a visual stimulus - a flash of light, for example - varies from one occurrence to the next. If the same light flash was presented many times over, the eye's electrical signal to the brain was slightly different each time

"The key point he stressed is that whether you see something or not, and how reliably you see it, doesn't just depend on the magnitude of the electrical response, but how reproducible that response is," MacLeod said.

While much of Cohn's work in this arena was rather technical and analytical, MacLeod said, "some of it had immediate fun value - for example, his demonstration that visual sensitivity fluctuates during the heartbeat cycle, and his finding that depth illusions can occur on escalators."

For most of the past 15 years, Cohn worked in the field of transportation engineering, applying his knowledge of vision science to solve practical problems. With his understanding of the way the eye detects visual signals and passes that information to the brain, he was able to develop various kinds of warning systems that provide faster human reaction times.

"He was very good at imagining solutions to problems involving warning signals and warning signs," said Daniel Greenhouse, a UC Berkeley research scientist in vision science who worked with Cohn for nearly two decades.

In the late 1990s, Cohn was asked by the California Department of Transportation (Caltrans) to test the effectiveness of light-emitting diodes, or LEDs, in traffic lights. When he and the team in his laboratory showed that these low-energy light sources were at least as effective visually as standard incandescent units, Caltrans began switching to LED-based traffic signals across the state, resulting in huge energy savings.

Other inventions by Cohn and his laboratory team were a cone-shaped emergency warning light for highway work zone vehicles and a light bar that indicates that a vehicle is braking. Both create the perception of movement within their displays, making them more noticeable and resulting in faster human reaction times. Before he died, Cohn was investigating methods of making railroad crossings safer.

As widely respected as he was for his research, Cohn was equally admired for his service to UC Berkeley and his dedication to his students and colleagues, said those who knew him. He took on projects that required long hours, tact and patience, such as the initiation of an undergraduate program, Health Arts and Sciences, designed to provide a broad background for students interested in the field of health; the development of a joint program in medical education between UC San Francisco and UC Berkeley; and the management of a building remodeling program for UC Berkeley's Minor Hall when the School of Optometry moved there in 1992.

He was strongly committed to mentoring students from disadvantaged backgrounds or any student seeking to discover his or her academic passion, said his wife, Barbara A. Cohn, an epidemiologist with the Public Health Institute in Oakland, Calif. Years before programs like this were formalized by many colleges, he made his lab available to disadvantaged high school students considering attending UC Berkeley and to undergraduate students who needed experience, doing whatever he could to support them, she said.

"Ted Cohn was a creative researcher who was not only dedicated to his students and university service," said MacLeod, "but was equally enthusiastic and devoted to improvement of the world he lived in."

Memorial contributions for a mentorship fund for undergraduate students can be made to the "Ted Cohn Mentorship Fund for Undergraduate Research," in care of Congregation Beth El, 1301 Oxford St., Berkeley, CA 94709.

Plans are pending for a memorial celebration this fall of Cohn's life.